corrosiefatigue

Corrosion fatigue is a damage and failure mechanism in which a material subjected to cyclic mechanical loading experiences accelerated crack initiation and crack growth due to the presence of a corrosive environment. The combined action of stress and corrosion often reduces fatigue life compared with loading in air or in non-corrosive conditions.

The underlying processes involve electrochemical reactions at the material surface and at crack tips, leading to thinning of the metal near the crack, anodic dissolution, pit formation that acts as stress concentrators, and sometimes hydrogen embrittlement. In corrosive environments, the effective threshold for crack growth under a given stress range can be lowered, and crack growth rates can increase with temperature, humidity, and chemical aggressiveness. The result is a synergistic effect where corrosion accelerates fatigue crack initiation and propagation beyond what would occur from mechanical fatigue alone.

Typical materials affected include steel, aluminum alloys, titanium alloys, and nickel-based alloys, with seawater, chlorides, sulfuric acid, or humid air as common environments. Influencing factors include the stress intensity range and mean stress, loading frequency, environmental temperature, surface finish and residual stresses, protective oxide films, and microstructural features such as inclusions.

Assessment and mitigation involve environmental testing and life prediction using modified fatigue models that account for environmental effects, and strategies such as material selection, protective coatings, corrosion inhibitors, cathodic protection, and surface treatments to reduce crack initiation (for example, peening to introduce compressive residual stresses).